The invention relates to a semipermeable capillary comprising a tubular semipermeable wall made of membrane-forming material.
Such a semipermeable capillary is disclosed in DE-A-22 36 226. In the latter, a capillary is described which is composed in its entirety of spun polymer solution. Said spun polymer solution is brought into contact with a coagulation liquid. Depending on the direction of flow of the coagulation liquid through the wall, a very dense skin is produced on the inside or outside, while a porous structure is produced on the other side. The dense skin serves as semipermeable membrane layer and the porous structure as supporting material.
A disadvantage of this known capillary is that it is weak as a result of the lack of a reinforcement. As a result, the semipermeable wall can rapidly become damaged. In order to make such a capillary stronger, the wall thickness can be increased, but this increases the flow resistance appreciably, as a result of which the filtration characteristics decrease considerably.